A study released by The Lancet medical journal on Friday concluded that the disproportionately high rate at which unarmed black people die at the hands of police in the United States has a corrosive impact on the mental health of black Americans.

The frequency of these killings has been cited as symptomatic of deeply rooted racism, and is in any case perceived as such by most black Americans, they reported in The Lancet, a medical journal.

Senior author Alexander Tsai, an associate professor of psychiatry at Massachusetts General Hospital and Harvard Medical School told the AFP:

“We found that when police kill unarmed black Americans, there is mental health fallout that reverberates throughout the black American community. This finding is significant because it shows that the effects of these killings go beyond immediate friends and family”

Tallies kept by news organizations and researchers vary, but police have killed approximately 300 Black Americans – most of them unarmed – every year since 2014.

Over this period, blacks were roughly three times more likely than whites to be killed by police, and nearly five times more likely to be killed by police while unarmed, the researchers said.

Despite the fact that 61% of the US population identify as “white,” and only about 13% as “black”, statistics show that black Americans have proportionally more encounters with law enforcement, which in itself increases the opportunity for violent outcomes.

To probe the mental health effect of police killings of blacks on the larger black American population, Tsai and colleagues compared two sets of data.

One was a national, 2013-2015 telephone survey of more than 100,000 black American adults that asked how many out of the previous 30 days were marked by stress, depression and emotional problems.

The other was a state-by-state tally of police killings from the Mapping Police Violence database.

Using statistical analysis, the researchers found a strong link between more days of poor mental health and deaths at the hands of law enforcement occurring in the 90 days before the interview.

This “spillover” effect was strongest 30-60 days after police killings in or near the state in which respondents lived.

Extended to the US black adult population, the findings suggest that police killings of unarmed black Americans could account for up to 65 million excess days of stress or depression per year, on a par with the mental health burden associated with diabetes, the study found.

“Regardless of what is driving the disparate killings of black Americans, these killings have corrosive effects on population mental health among black Americans,” said Tsai.

“Police killings of black Americans – in contrast to police killings of white Americans – have a long, painful history and sociological meaning attached to them.”

“They undermine mental health among black Americans because they are a manifestation of structural racism,” he added.